An uninterruptible power supply (UPS) is well-known in the art as a device which accepts an electrical power input from the utility supply and supplies continuous, good quality electrical power to an appliance. The UPS's output supply to the appliance is unaffected by variations or interruptions to the utility supply. UPSs generally have communication with the appliance so that the status of the UPS may be monitored.
Some types of UPS have a configurable output voltage which can be set to the voltage required by the appliance and normally this would match the nominal voltage of the utility supply. The person installing the UPS must have knowledge of the local utility's nominal voltage and then spend time setting this voltage on each UPS being installed. There is a risk that the wrong voltage will be set or even that the voltage will not be checked and left at the factory default if the UPS appears to be functioning correctly at the time of installation.
Some types of UPS provide a bypass function which operates if the UPS detects an internal failure. The bypass function connects the power input of the appliance directly to the utility supply, thus bypassing the failed component in the UPS. However, there is a danger that when the bypass function operates the utility supply voltage is not within the range required by the appliance. To warn of this potential condition some UPSs will raise an alarm which indicates that, should the UPS need to bypass itself, the supply to the appliance will be out of voltage range. Appliances for which a continuous supply of power is critical may be designed to perform a controlled shutdown in the event of this alarm being raised so that a subsequent UPS failure would not result in an instant loss of power.
For convenience the voltage range used to raise the alarm described above may be calculated as a fixed percentage deviation from this nominal output setting. This means that a where such a UPS is shipped to a global market it must be configured to the local utility voltage to avoid this alarm being raised unnecessarily during normal operation.
While this alarm is appropriate for appliances which have a narrow range of acceptable input voltages, most data processing equipment will accept a much wider range of input voltages than any particular range implemented by the UPS. This means that the alarm will be raised even though the utility voltage is within the range acceptable by most data processing equipment. Even after the nominal voltage has been set correctly there may still be problems if, for example, the utility voltage varies by more than the range implemented by the UPS or the installation has a backup generator which supplies a different voltage from the utility. In these cases the UPS would raise an alarm when, in fact, the input voltage to the UPS is quite acceptable to the appliance.
One solution would be for the appliance to ignore the alarm raised by the UPS, but this has a number of drawbacks. The UPS will give a visual and audible warning of the alarm which may confuse the user if the appliance takes no action. In extreme conditions the utility voltage may really be outside the range acceptable to the appliance in which case a UPS failure would cause instant loss of power to the appliance.
A need therefore exists for an apparatus and method for configuration of a UPS wherein the above mentioned disadvantage(s) may be alleviated.